Magneto resistive Random Access Memory (MRAM) is an emerging technology that may be competitive with prior integrated circuit memory technologies, such as floating gate technology. The MRAM technology may integrate silicon-based electronic components with magnetic tunnel junction technology. A significant element in MRAM is the magnetic tunnel junction where information may be stored as memory. The magnetic tunnel junction stack (MTJ stack) has at least two magnetic layers separated by a non-magnetic tunnel barrier, where a first magnetic layer (the fixed layer) has a set magnetic property and a second magnetic layer (the free layer) has a programmable magnetic property. The MTJ can store information based upon the programmable state of the second magnetic layer. More particularly, if the fixed layer and the free layer have parallel magnetic poles, the resistance through the MTJ stack is measurably less than if the fixed layer and the free layer have anti-parallel poles, so parallel magnetic poles may be read as a “0” and anti-parallel poles may be read as a “1.”
In some embodiments, the free layer may be pre-programmed before an integrated circuit is incorporated into a device. Incorporation of the integrated circuit into a device often involves a packaging reflow process that solders components at about 260 degrees Celsius (° C.). The stability of information in the free magnetic layer degrades as the temperature increases, and the magnetization of the free layer may become demagnetized if the temperature becomes too high (i.e., reaches the curie temperature for the free layer). Note that a permanent magnet generally becomes demagnetized if it is heated to its curie temperature or greater. An energy barrier (Eb) of the free layer should be sufficiently high at the packaging reflow process temperature to maintain magnetism so the stored information is not lost. For example, an energy barrier of about 40 kbT (kb is the boltzman constant times temperature, where kb is joules per degree Kelvin, and T is temperature in degrees Kelvin, so kbT is expressed in joules) or greater at the packaging reflow process temperature is generally sufficient to retain magnetism in the free layer so stored information is not lost. However, conventional MTJ stack designs that increase the overall energy barrier also increase the footprint of the MTJ stack, the power consumption, and decreases the endurance.
Accordingly, it is desirable to provide integrated circuits with magnetic tunnel junctions having a free layer with an energy barrier that is less sensitive to temperature increases than traditional magnetic tunnel junctions. In addition, it is desirable to provide integrated circuits with magnetic tunnel junctions that are temperature stable but have a free layer with a relatively low energy barrier at low temperatures such that desirable footprints and operations are possible, and methods of producing such integrated circuits. Furthermore, other desirable features and characteristics of the present embodiment will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.